Comment 5 for bug 857089

@Adrian Wechner
You could achieve that design only by adding a pixmap to be used as sidebar background.
BUT the toolbar size could change depending on the font dimension, that means the gradient across the sidebar and the toolbar will work only on the font size was used to snapshot the pixmap you will use in the sidebar.

All you can do is using a flat dark color, for example, but that is not nice at all (still better white, IMHO).